Polypropylene  (PP) is the second most produced plastic in the world, after polyethylene (PU). According to Statista, global polypropylene production was approximately 79.01 million metric tons in 2022. 

They are both versatile and durable, and they are used in a wide variety of applications. Understanding the differences between PP and PU is important because it allows you to choose the right material for the job. 

Learn more about polypropylene and polyurethane now!

1. Properties of polypropylene

Picture 1. Polypropylene (PP) is a flexible material with numerous applications. 

1.1. Physical properties

Polypropylene (PP) is a thermoplastic polymer that is known for its lightweight, strength, flexibility, and heat resistance.
Appearance: PP is a white, translucent solid.
Lightweight: With a density of roughly 0.9 g/cm3, PP is one of the lightest plastics available. This makes it perfect for applications requiring weight reduction, such as automotive and aerospace.
Strong: PP is a tough and long-lasting polymer that resists impact, abrasion, and fatigue. It has equivalent tensile strength to steel at up to 48 MPa. As a result, it is perfect for applications requiring strength and durability, such as packaging and construction.
Flexible: PP is a versatile material that may be easily molded into an array of shapes. This makes it perfect for applications that require complex shapes, such as medical and consumer items.
Heat resistant: With a melting point of 173°C (343°F), PP is one of the most heat-resistant plastics on the market. Therefore, it is appropriate for applications involving high temperatures, such as food processing and automotive applications.

1.2. Chemical properties

PP is a non-polar polymer, which means that it is not very reactive with other chemicals. It is also non-toxic and does not support the growth of bacteria. This makes it highly resistant to a wide range of chemicals, including:

• Acids: hydrochloric acid, sulfuric acid, nitric acid, acetic acid
  
• Bases: sodium hydroxide, potassium hydroxide, ammonia
  
• Solvents: water, alcohol, gasoline, oil

The only chemicals that are known to dissolve PP are strong oxidizing agents, such as concentrated sulfuric acid and nitric acid.

1.3. Processing properties

Picture 2. PP is a thermoplastic, meaning that it can be melted and reformed.

 

Discover more about the versatility and performance of PP: PP Plastic: Everything you need to know 

2. Properties of polyurethane

Bayer and his team at IG Farben invented polyurethane in 1937. However, polyurethane was not mass-produced commercially until the 1950s.

Appearance: PU can be transparent, translucent, or opaque, depending on its formulation. It can also be colored or pigmented. 
Density: PU has a density of 1.1-1.2 g/cm3, which is slightly higher than water. 
Tensile strength: PU has a tensile strength of 2.4-4.8 MPa. This makes PU a strong and durable material that can withstand high loads.
Hardness: The hardness of PU depends on its formulation, but it can range from 20 Shore A to 85 Shore D. Shore A is a measure of the softness of a material, while Shore D is a measure of the hardness of a material. 

Picture 3. PU is excellent for applications requiring strength, toughness, and chemical resistance.

 PU is a very versatile material with excellent chemical resistance. It is resistant to a wide range of chemicals, including:

• Acids: Most common acids, including sulfuric acid, hydrochloric acid, and acetic acid, are resistant to PU.
• Bases: PU is resistant to the majority of common bases, including sodium hydroxide and potassium hydroxide.
• Oils and greases: PU is abrasion, oil, and grease resistant. This makes it perfect for applications containing oil and grease, such as automotive and industrial applications.
• Solvents: PU is resistant to the majority of popular solvents, including acetone and ethanol.

However, PU is not resistant to powerful oxidizing chemicals like hydrogen peroxide and nitric acid. These compounds can lead PU to degrade and lose its characteristics.

2.3. Processing properties

Polyurethane (PU) is a versatile material that can be handled via casting, injection molding, and extrusion.

• Casting is a straightforward method that entails pouring liquid PU into a mold and allowing it to cure. Casting can be used to create a wide range of forms and sizes, from simple blocks to sophisticated pieces.
• Injection molding is a more sophisticated procedure that includes pumping high-pressure liquid PU into a mold. Injection molding is a high-volume manufacturing process that can yield products with great precision and reproducibility.
• Extrusion is the technique of driving liquid PU through a die to generate a continuous length of material. Extrusion is a technique used to make PU films, sheets, and other continuous shapes.

The appropriate processing method for a given application is determined by the desired qualities of the completed product as well as the needed production volume.

Learn more about Polyurethane plastic: All information about Polyurethane resin 

3. Comparison of polypropylene vs. polyurethane

Here is a comparison of the key properties of polypropylene (PP) and polyurethane (PU)

Still can't find the plastic you need? Check out our wide selection of plastics: Different Plastic Types: What You Need to Know 

Picture 4. Colorful plastic polymer granules, the raw materials for many of the products we use every day.

3.1. Key advantages and disadvantages of polypropylene

Advantages:

• Lightweight and strong
• Water and chemical resistant
• Durable
• Recyclable

Disadvantages:

• Not as flexible as PU
• Can be more expensive than PU
• Not as good of an insulator as PU

3.2. Key advantages and disadvantages of polyurethane

Advantages:

• Very flexible
• Good insulator
• Durable
• Resistant to abrasion and tear
• Can be processed into a variety of forms

Disadvantages:

• Not as water resistant as PP
• Can be more expensive than PP
• Not as recyclable as PP

To choose the right plastic for the job, it's important to know the pros and cons of PP and PE. Understanding the differences between these two common plastics can help you save money, make better products, and reduce your environmental impact.

4. Applications of polypropylene

Giulio Natta and Paolo Chini discovered how to make isotactic polypropylene, a better polypropylene, in 1954. This breakthrough transformed the plastics industry and resulted in the widespread usage of polypropylene in a variety of applications.

4.1. Food packaging

Picture 5. Frozen food, packaged in PP plastic, to keep it fresh and safe.

PP is a lightweight, durable, and flexible material that is resistant to grease and moisture. This makes it ideal for food packaging applications. PP is also non-toxic and resistant to bacteria, making it a safe choice for food packaging.

4.2. Medical devices

PP is also used to make a variety of medical devices, such as syringes, surgical instruments, and implants. PP is non-toxic, resistant to bacteria, and durable, making it a safe and effective material for medical devices.

4.3. Automotive parts

PP is used to make a variety of automotive parts, such as bumpers, fenders, and interior trim. PP is lightweight, durable, and impact-resistant, making it a good choice for automotive parts.

4.4. Textiles

PP is used to make a variety of synthetic fibers, such as polypropylene fiber, which is used in carpets and other textiles. PP fiber is lightweight, durable, and resistant to moisture and chemicals.

4.5. Building materials

Polypropylene is also used in a variety of building materials because it is durable and weather-resistant. It is also resistant to mold and mildew. Polypropylene is used to make a variety of building materials, including roofing materials, siding, and insulation.

5. Applications of polyurethane

5.1. Grocery bags

PE is a lightweight and durable material that is inexpensive to produce. This makes it ideal for grocery bags and other disposable plastic products.

5.2. Pipes and fittings

PE is also used to make pipes and fittings for a variety of applications, such as water supply, irrigation, and drainage systems. PE is durable and resistant to corrosion, making it a good choice for these applications.

5.3. Stretch film

Picture 6. Protecting furniture with PE plastic stretch film.

PE stretch film is a thin, transparent film that is used to wrap and protect products during shipping and storage. PE stretch film is strong and flexible, and it can be stretched to conform to the shape of products.

5.4. Toys

PE is also used to make a variety of toys, such as dolls, action figures, and balls. PE is durable, impact-resistant, and non-toxic, making it a safe and fun material for toys.

6. Bringing polypropylene and polyurethane to the world

Picture 7. Plastic granules recycled into new products, a circular economy in action.

6.1. Sustainability

Both PP and PE are recyclable materials, but there can be a difference in recyclability between the two materials for certain applications. For example, PP is more easily recycled than PE in some communities.
PP is also more difficult to produce than PE, which requires more energy and resources. However, PP is more durable than PE, which means that it can be used to make products that last longer. This can reduce the need to replace products as often, which can save energy and resources in the long run.

6.2. Development

A study from the United Nations Environment Programme (UNEP) found that plastic can have a positive impact on the development of nations. The study recognizes that PP and PE can improve people's lives by providing access to clean water, food, and shelter. 
Here are some particular examples of how PP and PE are already being used to create a beneficial impact in still developing countries:

• PP food packaging keeps food fresh and safe for extended periods of time, which can reduce food waste and increase nutrition.
• People in distant places with limited access to hospitals and clinics benefit from the usage of PP medical equipment.
• People in developing countries utilize PE pipes and fittings to supply clean water and sanitation.
• Stretch film and PE grocery bags can be used to prevent food waste and improve the transportation of items.

The optimist is justified. PP and PE are currently widely utilized in poor nations, and their potential to improve people's lives is enormous. We should expect to see even more novel and profound applications for these materials emerge as technology advances.

6.3. Environment

PP and PE are both relatively low-impact plastics, but there are some differences in their environmental impact. For example, PP is more difficult to recycle than PE.
PP and PE can also contribute to environmental problems such as pollution and climate change. When PP and PE are not disposed of properly, they can end up in landfills and incinerators, where they can release harmful pollutants into the environment.
PP and PE can also contribute to climate change because they are made from petroleum, a fossil fuel. The production and consumption of fossil fuels releases greenhouse gases into the atmosphere, which contribute to climate change.

7. Conclusion

Both PP and PU are valuable materials with a wide range of applications. When choosing between PP and PU, it is important to consider the specific properties and requirements of the application. PP is a good choice for applications where lightweight, durability, and flexibility are important. PU is a good choice for applications where strength, resilience, and chemical resistance are important.
Visit EuroPlas website today to learn more about the different types of plastic, their properties, and their applications. We also have a variety of resources to help you find the right plastic solution for your business needs.